1. Field of the Invention
The present invention relates to a two-stage screw compressor and a refrigerating device.
2. Description of the Related Art
Japanese Laid-Open Patent Publication (Kokai) No. 2007-40294 discloses a two-stage screw compressor which includes a box body forming a flow passage connecting an outlet of a first-stage compressor and an inlet of a second-stage compressor, and the box body stores gears which drive rotor shafts of the first-stage and second-stage compressors. In this screw compressor, a drive shaft which drives the gears driving the rotor shafts of the first-stage and second-stage compressors passes through the box body, and a mechanical seal is provided at a pass-through portion of the drive shaft to seal a compressed fluid.
However, it is not easy to completely seal a rotating shaft, and, when a toxic refrigerant such as ammonia is to be compressed, the refrigerant cannot completely be sealed only with this mechanical seal, and there is a problem that the refrigerant leaks.